Apparatus for making insulated electromagnets



y 4, 1940. E. H. BRANSQN 2,201,130

APPARATUS FOR MAKING INSULATED ELECTROMAGNETS Original Filed Jan. 15, 1935 FIG.1. A F

Vacuum Pump Condenser INVENTOR E. H. Bronson,

HIS ATTORNEY Patented May 14, 1940 NlTEZ. STATES PATENT OFFICE APPARATUS. FOR MAKING INSULATED ELECTROMAGNETS Edward H. Branson, Rochester, N. Y., assignor to General Railway Signal Company, Rochester,

2 Claims.

This invention relates to electromagnets and the apparatus for making the same.

This applications is a division of my pending application Ser. No. 1,924, filed January 15, 1935, for Insulated electromagnets and method of making the same, now Patent No. 2,091,234, dated August 24, 1937.

In railway train control apparatus and the like, certain coils, such as the car-carried train control receiver coils, are subjected to severe shocks and vibration and are exposed to moisture, acid and other deteriorating foreign substances. It has consequently been found expedient to com.- pletely enclose such coils by a covering of rer silient material, such as vulcanized rubber, which covering is in turn protected by a suitable coating which is resistant to acids and other detericrating foreign substances.

It has been found however that the ordinary methods of vulcanizing the covering after being applied around such coils causes the rubber to blister and often forces the rubber out at the ends of the coils underneath the outer protecting layer of material, and during vulcanization of the enclosure for the coils, considerable solvent vapors and moisture develop which are trapped within the windings and later causes short-circuits and deterioration to the winding insulation. It has also been found that the covering around the coils is not uniformly vulcanized by'the ordinary methods as considerable time is necessary for the heat to penetrate to the inner or core covering of the coils, which results in the outer covering being more thoroughly vulcanized than the inner.

In View of the above and other considerations, it is proposed in accordance with the present in vention to provide an electromagnet as well as the apparatus for making the same which is substantially free from moisture, solvent vapors and other deteriorating substances, and which is also protected against subsequent entrance of such substances therein. It is further proposed to provide such apparatus for vulcanizing the covering of electromagnets whereby the resulting covering is uniformly vulcanized around both the inner and outer surfaces, and wherein the covering material is of uniform density and thickness as well as free from air pockets and blisters.

Other objects, purposes and characteristic fea tures of the invention will appear as the description thereof progresses, during which, references will be made to the accompanying drawing which shows the invention in a manner to make it easily understood rather than with the view to showing the particular construction preferably employed in practice, and in which:

Fig. 1 is an elevational View of a core with insulation applied thereto preparatory to the winding of the coil thereon with parts of such insulation broken away to more clearly show the arrangement thereof.

Fig. 2 is an enlarged sectional view showing a portion of a coil upon the core of Fig. 1.

Fig. 3 is an elevational view of the completely covered electromagnet preparatory to vulcanization, with various parts thereof broken away to illustrate the arrangement thereof.

Fig. 4 is a diagrammatic and conventional view illustrating the apparatus employed in vulcanizing the covering around the coil of Fig. 3 in accordance with the present invention.

Fig. 5 is an enlarged'sectional view of a portion of a completed electromagnet constructed in accordance with the present invention.

Referring now to the drawing, a magnetic core I is shown with a pole piece 2 attached thereto, such as by welding, or of course these parts may be integral. shapes and of solid or laminated construction according to the requirement, and the top portion may be adapted to retain a suitable member for holding a coil upon the body of the core I. The coil retaining means in the particular core construction chosen for the present disclosure includes an end washer 3 of suitable rigid insulating material, which in assembly, fits over the end of the body of core I and is retained. by suitable brackets 4 clamped to the opposite sides of a reduced end of core I by bolts 5.

Before assembling the washers 3 and brackets 4 upon the core I however, the core I, pole piece 2 and washer 3 are all sand blasted and thoroughly cleaned with benzine, or the like, after which the body surface of the core I, inner surface of washer 3 and the inner surface of pole piece 2 are all coated with. two coats of rubber priming cement, such as the type sold under the trade name of Vulculock, which is followed by two coats of suitable rubber cement, with a drying time of approximately 15 minutes allowed between each of such coats.

A large Bakelite-varnish impregnated cloth ring 8 is now placed over the core and pressed down tightly against the inner surface of the pole piece 2, as shown, and a smaller washer 9 of uncured rubber having an outside diameter slightly larger than the completed coil and an inside diameter approximately equal to the diameter of core I, is placed over the core I and Thiscore I may be of various other pressed down and cemented tightly on the washer 3. The inside diameter of the ring 8 is sufficiently greater than the inside diameter of the washer to allow an inner circular portion of washer ll which is within the hole in ring 8 to cement to the pole piece 2. A second Washer IQ of uncured rubber similar to the washer 9 is now pressed down and cemented ti htly on the end washer 3, and the washer 3 together with washer ill is now placed on the end of core I and the brackets i are assembled as shown in Fig. l.

A sheet of uncured rubber i3 is now wrapped around the body of core i, which sheet of rubber i3 is to be wide enough to abut the rubber washers S and Hi and along enough so that its ends slightly overlap. In wrapping the rubber sheet IS, the surface should be kept clean and should be carefully ironed in place with the suitable tools to eliminate all air pockets and to fit tightly against the end washers 9 and iii. Strips of uncured rubber (not shown) may be applied around each end of the sheet is in a manner to reenforce the joints between this sheet l3 and the rubber washers 9 and Ill.

In order to protect the outer portion of the rubber washers 9 and id from dirt while winding the coil, narrow rings l i of thin material such as linen are applied to each surface of the outer portions of these washers 9 and 10. Two varnished cambric washers l5 having inwardly extending flanges around their inside circumferences are placed over the core and pressed tightly against the inner surface of the rubber washers 9 and i respectively. Inasmuch as it has been found expedient to assemble these washers l after the rubber washers 9 and I 0 have been sealed to the core covering 13, it is necessary to cut one side of the washers l5 thereby allowing their in stallation by twisting in a manner to open this cut sufliciently to slide over the body of core I.

A hole through a mid-portion of the end washer 3 is slightly counter-bored, and a hole of the same size in register therewith is cut through both the rubber washer l0 and washer to receive a flanged bushing i2 constructed of insulated material. The outer surface of the bushing i2 is first thoroughly coated with both priming and rubber cement and a small varnished cambric washer I l is cemented to the flanged end of bushing l2, after which the smaller end of bushing i2 is placed through the holes in washers l5, l0 and 3 so that its inner flange presses the surrounding portion of washers I0 and I5 into the counter-bored portion of washer 3 as shown in Fig. 1.

A sheet of varnish impregnated cloth I6 is now wrapped around the body of the core I over the rubber sleeve l3 so that its edges overlap the inner flanges of washers IS. The ends of the cloth it should overlap slightly and these overlapping end portions are cemented and temporarily bound with a few turns of tape until the coil is wound thereover,

In winding the coil a suitable machine of any well known type may be used and of course the size of wire and number of turns are to be chosen in accordance with the requirements of the particular application. The insulation on the Wire used in the present coil should be impregnated with insulating varnish before winding. During the winding of the coil, vents or air passages are formed for conducting vapors from within the coil to the outlet provided by the bushing l2. These passages may be conveniently formed by inserting fibre strips 2|] in intermediate portions of the coil during winding thereof, the strips extending the full length of the coil and separat ing the layers of the winding in a manner to form voids or passages adjacent each edge thereof. One of the strips 20 is located as shown in Fig. 2 so that the void in the winding formed at an edge thereof aligns with the hole in the bushing l2 (represented by the dotted circles), and another strip 20 (not shown) may be similarly located in the windings at a position diametrically opposite.

In winding the outer layers of wire, an annular recess, or space, having a lesser outside diameter than the center of the completed winding, is left at each end adjacent the washers 9 and ill for a purpose which will later be obvious. The method of bringing out the coil ends or leads is not herein shown in detail, but it has been found expedient to cover the beginning of the coil or the first turn with varnished cambric tubing, and in bringing this lead to the outer surface, a radial slot (not shown) may be provided in the end washer 3 into which is pressed the rubber washer H] to allow this bottom lead to be brought to the outer surface of the coil through this slot in order to prevent it from interfering with the other turns of the coil. The outer end is preferably terminated diametrically opposite the inner end, and flexible rubber covered lead wires 23 may be soldered to these coil ends, which lead wires 23 are brought around the outer top surface of the coil to a common point as shown in Fig. 3.

The lead wires 23 are cleaned thoroughly and wrapped with rubber tape, after which these leads 23 and the entire outer surface of the coil is coated with rubber priming cement and allowed to dry. A sheet of uncured rubber 24 similar to that applied to the core I is now tightly wrapped around the entire outer surface of the coil, beneath the extending portion of leads 23 as shown. The ends of the sheet 24 should overlap to form a tight joint, and should be carefully ironed down with suitable tools, making sure that all air pockets are removed. In ironing down the sheet 24, the edges are rolled down into the peripheral recesses left at the ends of the winding.

The linen protecting rings H are now removed from the rubber Washers 9 and I0, and the extending portions of these washers are thoroughly cleaned and then folded inwardly over the portion of the rubber covering 24 which enters the peripheral recesses and ironed down tightly in order to knit thoroughly thereto, thus making the outer surface of the coil of substantially uniform diameter throughout, as shown in Fig. 3.

The leads 23 are now placed part-way down the sides of the coil covering 24, as shown, and rolls of uncured rubber are placed tightly around the sides of the leads 23, and the point at which the leads leave the coil is also carefully sealed and re-enforced by pieces of uncured rubber. A small square of uncured rubber 25 is placed over the leads 23 and rolled down tightly to the coil covering 24.

The entire outer surface of the coil may now be temporarily covered with water-soaked cotton tape (not shown) wound tightly thereon while wet and tied. The coil is then allowed to stand overnight, during which time the wet tape dries to apply pressure to the rubber covering with the result that the rubber covering is compressed evenly and to a predetermined dimension.

When the cotton tape has thus dried, it is removed from the coil and the extending portions of the washer 8 is notched and folded inwardly over the rubber coil covering. The outer surface of the coil covering is now coated with a suitable rubber cement followed by a covering of rubberized tape 26 wound tightly over the rubber coil covering. In order to more thoroughly compress the coil covering, water-soaked cotton tape may again be temporarily applied in the same manner as before but over the rubberized tape 26, and the vulcanizing of the rubber covering should be started while this cotton tape is still wet in order to permit the shrinkage of the tape to compress the rubber covering against the windings during vulcanization.

The apparatus required for vulcanizing the rubber covering of the coil in accordance with the present invention includes an oven diagrammatically represented by the dotted rectangle enclosing the coil in Fig. 4, which oven should be thermostatically regulated and capable of maintaining a temperature of 275 Fahrenheit, with provisions included therein for conducting electrical energy from an external source into the interior thereof, and also with an external conduit 30 arranged for conveniently connecting to the threaded hole in the bushing 12 of the coil being vulcanized. Of course in practice an oven will be provided which will accommodate several coils at one time, and consequently a manifold within the oven will be provided and'connected suitably to the conduit 30.

A vacuum pump P is also required and is connected to the conduit 39 through a suitable condenser as shown. The outlet 30 is arranged to be connected either to the vacuum pump P and condenser or to an air drier by valves A and B, which air drier may be of the calcium chloride type. The interior of the oven used in vulcanizing the present coils should be heated to a temperature of 275 Fahrenheit prior to placing the coil therein, and while the coils are being placed therein, the temperature should not drop below 200 Fahrenheit.

In arranging the coils in the oven, the leads 23 are connected such as by a suitable receptacle or plug connecting means to the external electrical circuit including an ammeter A and a switch S, whereby current of a predetermined value may pass through the windings of the coil from an energy source, conventionally indicated by the symbols 13+ and B. The conduit 30 within the oven is also connected to the threaded bushing l2, and it is necessary to make all of these connections as quickly as possible so that the temperature within the oven does not fall below 200, otherwise the time required to again raise the temperature to 275 will be greatly increased.

When the coil is thus arranged in the oven, current is passed through the windings of a value which is found toheat the coil throughout in a period of one hour to a temperature of 275 Fahrenheit. The value of this current must of course be predetermined in accordance with the total resistance and the size of wire used in the coil.

With this current flowing in the windings of the coil, the valve A is closed, valve B is opened and a third valve C is opened sumciently to allow the vacuum pump P to maintain a vacuum corresponding to an absolute pressure of about 380 millimeters of mercury in the interior of the coil, while the temperature of the coil is being raised to 275. This condition is maintained for approximately one hour, after which time the electrical energy is removed from the windings of the coil by opening the switch S, and the valve C is fully opened to raise the vacuum within the still opened the coil is allowed to cool to room temperature.

When the coil has thus cooled to room temperature, the conduit 3E! is disconnected from the bushing l2 and the electrical connections removed from the leads 23. The threaded opening in the bushing l2 must now be closed immediately, and if it is not found to be practical to permanently close this opening immediately, a temporary plug may be inserted. The method of permanently closing the opening in the bushing 12 is shown in the enlarged sectional view in Fig. 5, and consists in first thoroughly coating the entire inner surface of the threaded hole with one coat of rubber priming cement followed by one coat of suitable rubber cement, with a drying time of approximately 10 minutes left between these applications, after which, a disc of uncured rubber 32 is pressed into the hole in the bushing l2 and further forced down and retained by a threaded fibre plug 33. The temporary covering of cotton tape is now removed and the coil covering is finally completed by the application of two coats of suitable acid-proofing paint to the entire outer surface.

The present invention provides a novel arrangement of apparatus whereby vulcanization of the coil covering is greatly expedited by heating from within the coil by passing electrical current through its windings, and whereby the removal of all moisture is insured by evacuating the interior of the coil during vulcanization, and finally the pressure within the coil covering is raised to atmospheric by incoming air taken through an air drier.

The coil thus vulcanized is then completely sealed against the entrance of moisture or air by tightly and permanently plugging the vent so that the completed coil may then be maintained indefinitely in its moisture-free condition. The apparatus used in vulcanizing the covering of the present coil has the further advantage of creating a difference in air pressure between the outside and the inside of the coil covering which results in a denser and more uniform covering of rubber. In other words, the vacuum within the coil results in a compressive effect of the normal air pressure on the outer surfaces, and of course, the possibilities of blistering of the coil cover ing due to the building up of pressure within the coil is entirely eliminated by the vacuum employed in the present process.

The above rather specific description of one form of the present invention is given solely by the way of example, and is not intended, in any manner whatsoever, in a limiting sense. It is also to be understood that various modifications, adaptations, and alterations may be applied to meet the requirements of practice, without in any manner, departing from the spirit or scope of the present invention, except as limited by the appended claims.

What I claim is:

1. Apparatus for vulcanizing hermetically sealing rubber coverings around electromagnets,

comprising, a heating oven capable of enclosing an electromagnet, circuit means for applying electrical energy to the winding of the electromagnet while the magnet is in the oven for heating the spaces between the turns and between the layers of the magnet winding, a conduit, means connecting the conduit with the interior of the elcctromagnet winding while it is in the oven, a vacuum pump and an air dryer, each associated with the conduit, and means for connecting the vacuum pump and the air dryer to the conduit for, respectively, forming a partial vacuum in the space occupied by the winding and supplying dry air to said space.

2. Apparatus for vulcanizing hermetically sealing rubber coverings around electromagnets,

comprising, a heating oven capable of enclosing an electromagnet, circuit means for applying electrical energy to the winding of the electromagnet while the magnet is in the oven for heating the spaces between the turns and between the layers of the magnet winding, a conduit, means connecting the conduit with the interior of the electromagnet Winding while it is in the oven, a vacuum pump and an air dryer, each associated with the conduit, and manually operable means for connecting the vacuum pump and the air dryer to the conduit for, respectively, forming a partial vacuum in the space occupied by the winding and supplying dry air to said space.

EDWARD H. BRANSON. 

